Tinder's Terms of Service (TOS) is pretty clear:
Therefore, you agree not to:
• use the Service or any content contained in the Service for any
commercial purposes without our written consent.
• copy, modify, transmit, create any derivative works from, make use
of, or reproduce in any way any copyrighted material, images,
trademarks, trade names, service marks, or other intellectual
property, content or proprietary information accessible through the
Service without Tinder’s prior written consent.
• use any robot, bot, spider, crawler, scraper, site search/retrieval
application, proxy or other manual or automatic device, method or
process to access, retrieve, index, “data mine,” or in any way
reproduce or circumvent the navigational structure or presentation of
the Service or its contents.
• modify, adapt, sublicense, translate, sell, reverse engineer,
decipher, decompile or otherwise disassemble any portion of the
Service, or cause others to do so.
• use or develop any third-party applications that interact with the
Service or other users’ Content or information without our written
The Company may investigate and take any available legal action in
response to illegal and/ or unauthorized uses of the Service,
including termination of your account.
If you ignored that and did your machine learning research with images anyway, you're breaking the TOS, and to be honest, you may not be caught. But if you published your research, Tinder could demand you engage in arbitration or sue you on the premise that your research proves you violated their TOS.
If your jurisdiction is outside of the US, other laws may come into play, but it's safe to assume you could still be in legal jeopardy from Tinder.